Systematic design of wideband ΔΣ modulators for WiFi/WiMAX receivers

• Published in: Analog integrated circuits and signal processing Vol. 65; no. 2; pp. 197 - 208
• Main Authors: Malla, Pukar, Lakdawala, Hasnain, Naiknaware, Ravi, Soumyanath, Krishnamurthy, Kornegay, Kevin
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.11.2010
• Subjects: Circuits and Systems; Electrical Engineering; Engineering; Signal,Image and Speech Processing; ADC; Delta sigma modulator; WiMAX; Receiver; WiFi; Multi-standard
• ISSN: 0925-1030; 1573-1979
• DOI: 10.1007/s10470-010-9471-y

Modern multi-standard receivers in deep-submicron technologies pose significant design challenges on the analog baseband. Moving this analog filtering to the digital domain simplifies the design, yielding a process-scalable implementation. However, analog-to-digital converter (ADC) specifications now become more stringent and must be obtained by comprehending the standard and the system. Assuming a receiver NF of 5.96 dB and SNR degradation of 0.36 dB by the ADC, the proposed dual-mode WiFi/WiMAX receiver attains an input sensitivity of −74 dBm (20 MHz channel bandwidth). To accommodate the high dynamic range and the anti-alias rejection needed for the system, a Delta-Sigma (ΔΣ) ADC is proposed. Single-loop and Multi-Stage Noise-Shaping (MASH) architectures that achieve a SNR of 69 dB at a low oversampling ratio (OSR) of 8 for a conversion bandwidth of 40 MHz (108 Mbps, OFDM) are investigated at system level. Based on thermal noise, harmonic distortion, and power tradeoffs, a ΔΣ ADC design that meets the design specifications is presented.